Resistance spot welding may be used to join steel substrates. In general, resistance spot welding may include clamping a workpiece, e.g., the steel substrates to be joined, between two electrodes with a force, and passing an electrical current from one electrode, through the workpiece, to the second electrode for a time period to thereby complete an electrical circuit. The electrical current generates heat from electrical resistance within the workpiece at both electrode-to-workpiece and substrate-to-substrate faying interfaces. The heat momentarily melts the steel substrates at the substrate-to-substrate faying interface to form a weld nugget, i.e., a spot weld joint, and thereby joins the steel substrates.
Spot weld joints formed via such welding may fatigue when subjected to many cycles of tensile shear load. However, spot weld joints which are substantially free from cracks, especially cracks that originate from the substrate-to-substrate faying interface, generally exhibit excellent weld strength and fatigue life.